----Do you know our hometown at all?----No, this is the first time I _____ here.
There is a natural phenomenon scientists call the greenhouse effect.
Every time I returned after an , I felt stupid because I was behind the others.
However, the eruption itself is really exciting and I shall never forget my first sight of one.
I go back to sleep when suddenly my bedroom became as bright as day.
It is human activity has caused this global warming.